OBJECTIVES: A. Circular layer of the rat myometrium will be studied with respect to: 1. Comparison of membrane electrical activity and contractions during electrical stimulation and after partial membrane depolarization by potassium. 2. Correlation of circulating levels of estrogen with electrophysiological changes in the muscle at various times in gestation. B. Initiation of experiments concerned with the release of norepinephrine (NE) in the oviduct of the rabbit during adrenergic nerve stimulation: 1. Release of 3H-NE during nerve stimulation after previous incubation of oviduct with 3H-tyrosine. Oviducts isolated from rabbits at various times after ovulation. 2. Record oviductal contractions simultaneously with 3H-NE release measuements. 3. Measurement of NE contents in samples of oviducts used in each experiment.